Interleukin-4 (IL-4) is a natural protein which has been discovered recently and which is believed to have a therapeutic potential against infection, cancer and autoimmune disease. Human IL-4 is reported by Yokota et al., Proc. Natl. Acad. Sci. USA, Vol. 83, pages 5894-5898 (1986). Mouse IL-4 is reported by Lee et al., Proc. Natl. Acad. Sci. USA, Vol. 83, pages 2061-2065 (1986), and Noma, et al., Nature, Vol. 319, pages 640-646 (1986).
Recombinant DNA techniques have been applied to the discovery of IL-4 as well as to the creation of bacteria which are capable of expressing IL-4. This has opened the way to large scale production of IL-4 which is required to investigate, develop and realize the therapeutic potential of this protein. However, clinical use of IL-4 requires high purity material that is not contaminated by cell constituents or cell debris of the IL-4-expressing cell. Accordingly, extraction of IL-4 from the cells of IL-4 expressing bacteria in sufficiently high purity and yield is required.